Cooling is the main content of PCB thermal design. The  purpose of heat dissipation in the component temperature exceeds the  reliability guarantee temperature, take appropriate cooling measures, so  that the temperature dropped to the reliability of the working range. PCB heat dissipation mainly from the thermal conductivity, convection, radiation to carry out three aspects. This article describes the PCB circuit board cooling design techniques
First, the components arranged heat.
1, the components arranged to meet the cooling requirements
Staggered arrangement. In  layout design components layout, should be heating components and  general devices and temperature-sensitive devices to distinguish between  the heat around the device should be left adequate cooling gas flow  channel, heating elements should be staggered distribution. This is usually the same arrangement of the normal arrangement of the opposite, help to improve the cooling effect. In this case,
When  the thermal performance of different components of the mixed  installation, it is best to heat the components installed in the wind,  the heat exothermic components installed in the wind, or heat-resistant  components will be in the path of heat dissipation, its The result is a higher temperature at the part where the heat resistance is poor. When  the heat-resistant elements are arranged at the same level, the order  of arrangement is that the power consumption is high, and the components  having poor heat dissipation are placed in the upwind. In this case,
2, the high heat devices heat
When  a small number of components in the PCB when the heat is large, can be  added in the heating device on the radiator or heat pipe, when the  temperature can not come down, you can use a fan with a radiator to  enhance the cooling effect. When  the amount of heating device is large, you can use a large heat shield,  which is based on the PCB board heating device location and level of  custom heat sink or in a large flat radiator to cut out the different  components of high and low position. Place the heat sink over the component surface, and contact each component to dissipate heat. But because of the high and low consistency of components when welding poor, heat dissipation is not good. Usually in the component surface plus a soft thermal phase change thermal pad to improve the cooling effect.
Second, PCB circuit board cooling
PCB  board is copper / epoxy glass cloth substrate or phenolic resin glass  cloth substrate, there are a small amount of paper-based copper clad  sheet. Although  these substrates have excellent electrical properties and  processability, they have poor heat dissipation, and the heat  dissipation path of the high heat generating element is to dissipate  heat from the surface of the element to the ambient air. But only very small surface area of the component surface to heat is not enough. At  the same time as the heat generated by a large number of components  passed to the PCB board, so the best way to solve heat dissipation is to  increase direct contact with the heating element of the PCB's own  cooling capacity, through the PCB board out or distributed out. In this case,
1, the choice of good heat dissipation plate
Epoxy glass cloth sheet thermal conductivity of a 0.2W / m ℃. Ordinary  electronic circuit due to heat a small, usually epoxy glass cloth  substrate production, the heat generated by a small amount of heat  through the alignment of the general design and components themselves  distributed out. With the miniaturization of components, high integration, high  frequency, the heat density increased significantly, especially the use  of power devices, in order to meet this high heat requirements later  developed a number of new thermal conductivity sheet.
2, the use of reasonable alignment cooling
Because  of the poor thermal conductivity of the resin in the sheet metal,  copper foil and the hole is a good conductor of heat, so to improve the  copper foil remaining rate and increase the thermal hole is the main  means of cooling. PCB  heat dissipation capacity, the need for thermal conductivity of  different PCB insulation substrate with the equivalent thermal  conductivity calculation. The thicker the copper foil, the higher the residual rate of copper  foil, the more the number of layers, the greater the equivalent thermal  conductivity, P C B board, the better the cooling effect.
PCB thickness direction of the thermal conductivity coefficient of thermal conductivity than the surface is much smaller. In order to improve the thermal conductivity in the thickness direction, a heat conduction hole may be used. The thermal vias are through: the metallized holes of the PCB. The  effect is equivalent to a thin copper tube along the PCB thickness  direction from its surface through the PCB is the back of the heat  conduction, heat the heat back to the PCB quickly escape or conduction  to other thermal layer. Such  as IC mounted on the bare chip in the PCB, PCB board in the bottom of  the set of numerous thermal holes of the design program is gaining  popularity. Therefore,  in the PCB alignment to improve the cooling capacity, should be thick,  thick copper foil, thin, multi-layer, large area of copper, plus  thermal hole design